12au7 cathode follower schematic The schematic shows 300 Volts B+. I've got a Navships manual and in it are a bunch of what the US Navy called pulse cathode followers. Some direct coupled experimental discussion schematic I would say. The cathode load in this case are the 10k + 47k resistors, in series. Note the very sturdy parallel-cathode-follower output (the 12AU7 section). A 6SN7 has 2600 to 3000 uMhos. If you are driving 600 ohms to Pro levels, the 12AU7 just won't do well. 06 of the supply voltage as load swing. Common-cathode (a. 6DK6-based Cathode Follower OTL May 24, 2021 · It uses a 12AU7 as a cathode follower for the input, I've modified it by adding an EF86 in triode mode at the end, which should give a modest gain, but make up for the losses in the tone stack. But cathode follower output impedance is low, which makes it a decent output stage. If one is a cathode follower, the other half has to be a voltage amp. Sep 9, 2023 · The issue involves a cathode follower circuit I'm designing that will use a 12AU7. 2. The reader, Arief, who sent me the schematic had no knowledge of its source, but he heard that it was a headphone Oct 13, 2006 · In the schematic below, we see both a cathode follower and a White cathode follower with extra cathode resistors. Would splitting up the first stage plate resistor (R4) and making it a split The top valve is a self-biassed cathode follower that has its input capacitively coupled from the anode of the common cathode lower stage. Feb 2, 2023 · V2 = ECC82/12AU7 V3 = ECC82/12AU7 Cathode follower outputs on the right drive grids of 6 x 6550s in 2 sets of 3 push pull. I'm still working out the particulars of the power supply. I looked at the mu-follower too. I have NO idea why there is a cathode follower on front. If high-gain was never our goal, but a medium-gain line-stage amplifier, then the following design is the better way to go, as it offers the same gain as the original SRPP-cathode-follower-based circuit, but delivers a greatly improved PSRR due to the Aikido cathode follower output stage. Aug 31, 2016 · The 12AU7 would be a better cathode follower, while the 12AX7 is a better voltage amp. With a 12AU7, this circuit had 0. With Rl= 600R, it really doesn't matter what the tail resistance is: 100K || 600R is still 600R, for all practical purposes. The Sallen-Key circuit was chosen for it's simplicity, and the Linkwitz filter is used so that the phase shift through the high-pass and low-pass sections are equal at the crossover frequency. Finally the second stage is bootstrapped to maximize gain/ output swing and PSRR. The 6. Notice that this time the The calculator calculates a cathode follower's unloaded voltage gain (the gain without being connected to the next stage) and output impedance based on the triode's characteristics and the cathode resistor value. . The plate impedance of a rich 12AU7 is about 10K-15K. In This Issue 1 4 8 9 11 14 18 Cathode Follower White Cathode Jan 4, 2010 · The original circuit uses 33K cathode resistors for the 12AU7 cathode follower (for some reason you have changed them to 330K in your schematic). Cathode follower with tube 12au7 (ecc82) schematic: +250vdc +b Cathode tube follower preamp white schematic tubecad followers build resistor cornet improvement referring left talkbass let 12au7 cathode follower schematic. Take a look at the attached schematic and let me know what you think. But I'm trying to figure out if using a triode other than that of the same tube (like a typical CF in guitar amps) will require special consideration to get similar Anode Follower SRPP The grounded-cathode amplifier inside the anode follower is purely single-ended in operation. I used a 3V battery in the above schematic to bias triode T3 That would be nice to use the 12AX7 for the amplfier and the 12AU7 for the cathode follower part. The 5963 is similar to a 12AU7. The 1M grid resistor is returned to the bottom of the "cathode bias resistor" instead of ground, with the cathode load between that point and ground. Choose the plate resistor value for V1. The problem, however, is that the buffer no longer operates in push-pull, having been transformed into a single-ended circuit, which means that the maximum current swing into the external load impedance is equal to the White cathode follower's idle current, not the twice the idle current that a true White cathode follower can deliver in push-pull. This XL version uses a White Cathode Follower buffer for about half… This is a high gain preamplifier that is suitable for use where a lot of gain is required - to drive a power amplifier that needs plenty of gain or perhaps for use with instruments, like a guitar or microphone. Only so many ways to get that done. The Leak TL-10 amplifier. The cathode follower therefore acts as a well-regulated voltage source to create a fixed DC grid bias for the LTP. The downside is the need for higher current capacity from the power supply. It may be "wrong" but some people like it. The Rout < 700r, and THD at 1Vac < 0. It runs on a +/- 100V (more or less) power supply. So I put a 12AU7 cathode follower at the end of the chain, and -1. 5 V. The cathode follower has negative voltage gain: the output voltage is less than the input voltage. Cathode-Follower OTL It seems as if every week, there's another schematic for me to review. Adjustable gain stage experiments (12ax7 +ecc88)Marshall schematic follower 12ax7 cathode amp result recommend folks cathod against why using do 30th anniversary board 12au7 cathode follower ccs checkCathode follower tube tubes voltage work something better would like volts only. Tube Power Amplifiers: Single Ended Hybrid 12B4 Anode Follower OTL (about 80mW output) 50C5 SET; 6BM8-based; 6L6 Headphones OTL; Direct Drive ESL (balanced SE output) "Horiz-OTL" Sweep tube C. ♦ PDF Cover Page ♦ Perkins Electro-Acoustic Research Lab, Inc. I already have 2 paris of 12Au7 which is an excellent tube for buffers as it will be unity gain stage cathode follower. - Key features of the BCF PCB include redundant solder pads, support for multiple heater voltages/tube configurations, and a push-pull topology that allows it to be used as a headphone . A common mistake on Fendery plans, using 1. I would also comment that with a 330K plate load resistor and a 100V plate supply, they are barely conducting. I did this because both the 4S and the cathode follower work better up there. However these tubes mainly date back to the days of mono so there is no reason that you cannot use a 12AT7 for the amplfier part of both channels and the 12AU7 for the cathode part of both channels. If you look at the full schematic Dec 25, 2024 · Thats why I was thinking some goofy NFB correction thing going on. Dec 11, 2009 · Complete schematic diagram of direct-coupled 6V6 cathode-follower amplifier. Applying a negative feedback loop transforms the SRPP into push-pull anode follower. Jul 12, 2019 · If you change the cathode resistor to 2K, then 1/(0. I suspect a schematic would answer most of these questions. Here is a picture of the setup. Input is fed to the grid, and output is taken from the cathode. You cant trust dc output. 95 Move the output to pin number 6. The SRPP, unlike the cathode follower, must be tuned to (optimized to) a specified load impedance. If the voltage across each 33K resistor is 155V as indicated in your schematic then the quiescent current through each cathode follower is about 4. A cathode follower is also known as a grounded plate amplifier, since the plate is kept at ground potential for RF. 1. The cathode follower, once again, does its job. 95 V. Peut-etre que ca Apr 8, 2002 · Of course it is a follower and will follow the input voltage, but for a very short period it will draw grid current if the signal swings too fast and too high. Key components include the 12au7 tube, resistors ranging from kiloohms to megohms, and capacitors from picofarads to hundreds of microfarads used for coupling and The other way to bias the cathode follower is by applying a fixed voltage to the grid. In other words, the ACF-2 greatly improves on the cathode follower's already fine PSRR. Which is pretty much how all the C12/elam style mics i built before Dec 15, 2017 · During my Dyna PAS hacking days, the 12AU7 always sounded gutsier in line stage and cathode follower applications than the 12AX7 because it had lower Rp and pulled more current. A fixed-biased cathode follower is more likely to behave the way you expect May 17, 2019 · The 12AU7 contains non-linear triodes. So Power dominates the stage that Jim is asking about. This could probably drive a 10K load pretty easily. In other words, it wasn't just requests that prompted my making this new PCB, as I, too, love the 6SN7 and Apr 4, 2018 · The regular Muchedumbre is an ultra-simple buffer with few parts and straightforward operation. For load resistor it's usually best to start at 2x internal plate resistance. The input volume control doesn't have to be 100K at any cost, it could be 47K or even a nice 20K ALPS RK27 Because the tubes are configured in a balanced totem pole, with equal cathode resistors, the cathode resistor's value need not be changed every time a different tube is used, as a wide range of tubes can use the same resistor value in this configuration. Two stage 12AU7 preamplifier with low impedance output stage. Jan 12, 2009 · Hi Sakis, The schemaric shows either a 12AX7 or 12AU7. Then we decide on a bias point and run the AC load line through it. Make sure that is the tube in the cathode follower socket. The differential input stage loads the bridges Another circuit was also tried - a simple plate loaded amplifier with a cathode follower output. I’ll post a power supply schematic shortly. Okay, let's go over again in greater detail. You will need double the heater current. I could not find any ready made schematic of any tube buffer available which i could directly implement using the 12Au7 tubes. If this is the case, then there will be little, or no Feb 19, 2024 · 12au7 schematic 12ax7 preamp preamplifier amplifier schematics vacuum tubed diyaudioprojects ecc82 cathode 6sl7Cathode tube follower preamp white schematic tubecad followers build resistor cornet improvement referring left talkbass let Cathode follower again ;)no rocket science!12ax7 schematic tube amp preamp preamplifier bass circuit diy kit This is done by splitting the previous stage's anode resistor into two equal parts and connecting a capacitor from the cathode follower's cathode, to the junction of the two resistors [see right]. You can go any which way. Av = mu / (mu + 1) Cathode followers are, generally, used as buffers - to isolate one stage from another, so their gain is less than unity. But when looking at the curves in the datasheets of the 12AU7 the bias for a current of 2. Now for the truly interesting addition: the two jumpers J4 and J5. Don't forget that an output coupling capacitor will be needed to block the cathode voltage from watever we happen to be plugging the cathode follower into. Nor a white follower. The cathode The 4S with a 12AU7 and the volume control on the input, has an output impedance 11. 12ax7 cathode follower schematic For such individuals, the 12AX7 & 12AU7 combination will realize a gain of 200 (+46dB), but the 12AX7 cannot compete in a low-noise race with the previously listed tubes. And since you don't have much voltage, that also means you will have to seriously limit the input levels. Dec 11, 2023 · Below is the stock Aikido linestage circuit topology. 3) Key aspects of the design My 5E3 Deluxe plugged into a 125V outlet has a B+1 voltage of 368, plate voltage of 360, plate-to-cathode voltage of 340, screen-to-cathode voltage of 300 and 20 volts on the cathode (-20 volt grid bias). And this is what a cathode follower looks like on a schematic. With -20db signal from my sound interface injected into the grid i get just 1. Apr 4, 2018 · If you’d like something with just a little more nerd sprinkled on top (and an extra 12AU7), try the following. Obviously you have some type of gain maybe op-amp circuit before the follower as you won't get any gain from the follower and may be only adding noise and you'll likely need a recovery stage after the tone stack to make up for the loss in the stack and the CF but Cathode follower has gain of 1. Title: Cathode followerwith 12au7 Created Date: 8/28/2013 7:56:17 AM Mar 7, 2024 · jai construit ce preamp cathode follower avec 12au7, mais jaimerais savoir si je pourrais mettre des 12ax7 a la place des 12au7 etant donné que jen ai un gros stock et aussi pour comparer . It can have an input resistance in excess of 10 Meg ohms and an input capacitance of less than 2 pf contributed by the tube. there is the full schematic for giggles. I don't really know how complicated a 12au7 per channel preamp could be. I don't like this tube but I have some nice NOS 12AU7's so I built this preamp. 5K instead of Leo's 820r, sets the voltage amplifier plate higher then the cathode follower can follow. 92 mA as the current of the first stage. 3Vdc negative power-supply rail allows us to supply both the constant-current source and possibly the tube's heater. But is said center bias can be found by Mu*cathode resistor value = plate load value, use load line plotter to prove. Jun 12, 2013 · With a cap at the cathode + a ccs, you'll have a lot of gain with an 12au7. However, looking at the curves you have 80V plate to cathode and 2mA plate current which should put the bias near 2V. It's a great beginners circuit for high voltage tube applications. My estimate values: RL = 3 kOhm RB = 200 Ohm RG = 100 kOhm Cin = 2uF Cout = 2uF Feb 5, 2011 · I don't think so and feel free to post a schemo if you want. You may want to have more headroom at the input. Had the FX send come off of the V2A cathode, that may have been what Merlin intended. The simplest buffer that can be made with tubes, it is used to match a signal from a high impedance source to a low impedance load. Dec 7, 2019 · of the 12AU7's cathode potential. All of this will give a DC operating point of about 2. Aug 11, 2012 · Here are the measurements of the circuit i made with cathode follower vs plate follower. The 12au7 ecc82 is a twin triode vacuum tube it is very popular in the audio world because it is rather rugged and can be operated at lower voltages. You will need the Vp (plate voltage) of V1 to be 1/2 of B+ voltage. As such, the type makes a poor voltage amplifier. However, the cathode follower is a device that can present a Lo-Z output, but only to a Hi-Z load. Nov 28, 2009 · Cathode follower 1/2 of a 12AX7 or a 12AU7 can be used as a Cathode follower. Jul 14, 2021 · I tried it with a ZVN0545 source follower, but the clipping was too sharp-edged. Aikido Cathode Follower The second stage in the Aikido Cascode is an Aikido cathode follower. If you change the cathode resistor to 560, then 1/(2*pi*R*C) is a pretty good estimate. So (15*15)/(20) is gain of 11. The other is the cathode-follower output from the 6V6. That is that the output follows the signal coming from the plate of the triode. I have also added balance controls and a tone bypass. a. The EF86 configuration is essentially based on the Svetlana preamp schematic. 9. The cathode follower then effectively multiplies or bootstraps the value of the lower anode resistor R2, making it look like a constant-current source. A higher negative bias voltage would be advisable, even for a cathode follower. Don't know the reasons why this tubet sounds good in mu follower and awful in a simple grounded cathode configuration (so don't ask me). Well, at least this week's circuit continues the thread from my last post on cathode-follower output stages, but differs by being an OTL. Most would agree that a 12aU7 makes a better follower 12AU7 (ECC82) Cathode Follower Tube Preamplifier Schematic This schematic below is a simple two stage line-level preamplifier using a single 12AU7 (ECC82) tube per channel. Changing from a 27k Ohm resistor to a CCS: Apr 30, 2020 · I have this old Ampex 1260, and found an old service manual, and it says “recommended load impedance of 250k ohms or greater. All 2nd harmonic. Aikido Cathode Follower [ACF] 6CG7, 6DJ8/6922A, 6H30, 12AU7, 12AT7, 12BH7, 5963, 5965, and ECC99. The input impedance of this follower is equal to the three 1M input resistors in parallel, i. Web cathode follower with tube 12au7 (ecc82) schematic: Web 12au7 (ecc82) cathode follower tube preamplifier schematic. 5 Rip = 6250 ohms Zout = 6250 / 19. The only reason I'd decided on the 12AU7 is that I had indeed read the 12AX7 made a crappy cathode follower; so if that's not the case I've definitely got no problem using the tube the PS and chassis were already designed to use. In addition, the ACF-2 produces a tad bit less distortion than comparable cathode follower by using the triode’s own nonlinearity against itself. Put a dozen 12AU7 together and you can run with a Champ (at far higher heater consumption). 12AU7 (ECC82) Cathode Follower Tube Preamplifier Schematic. 5 Av. ) of the cathode follower goes up too, makes the cathode follower a nonlinear load for the previous cathode bias gain Jan 4, 2014 · Without knowing you have taken a conceptual discussion schematic from glassware and tries to implement it. 6V CCS set to 6mA current My grid leak resistor is 510k, and Rb is still 470R, input cap is 680nf and output is 2. The cathode resistor is 250 ohm 5 watts and the output transformer plate-to-plate impedance is 8k (RLoad). In the schematic above, safety resistors have been May 24, 2011 · Bogen DB15 schematic. In contrast, the SRPP is a push-pull affair. The 4S with the cathode follower output buffer has an output impedance of 575Ω. 6 Cathode Follower. Nov 8, 2016 · Anyway, the usual assumption that cathode followers are simple circuits that have 100% negative feedback and therefore extremely low distortion isn't entirely true. Jun 3, 2004 · > 12au7 white cathode follower What are you driving? If only 10K and up, 12AU7 is not the ultimate choice but very good. Jan 13, 2022 · 12AX7 has poor drive capability, a 12AU7 or 12AT7 would be more appropriate, but they have different enough characteristics that it won't simply drop in to replace it without circuit changes in most instances. 7mA. The Cathode follows the signal on the Grid without amplifying it. Apr 26, 2024 · Tube 12au7 preamplifier preamp schematic diy amp valve amplifier circuit headphone guitar circuits schematics diagram electronics tubed electronic tubes tim12au7 (ecc82) cathode follower tube preamplifier schematic. A DIY hi fi preamp design from 1954. This does lead to large and very-varying grid current. A Cathode follower is often connected directly to the output of a high impedance Anode load pre-amp. SW, Calgary, AB; CAN T2T May 6, 2007 · 06 May 2007. I finally decided to design my own cathode follower using the 12Au7 tubes with the following V5a + V5b are triodes in 12AU7 and in cathode follower mode and work with a high amount of local series voltage NFB and the gain of about 12 without NFB is reduced to 0. 5 mA. The second stage could give an input impedance as high as anybody would need. I would like to get the gain lower, around 6. edit: remove the cathode bypass capacitor. A gain of ~15 is still way high in my view. Oct 11, 2018 · Small bias voltage values do not matter in a cathode follower because the cathode literally follows the grid signal so the bias voltage stays nearly constant. These two tubes are at opposite ends of the mu table 100 vs 20. 5 / (19. A 6SN7 is an octal tube that requires a different tube socket. With 12au7 20*2400 (single cathode value) = 48k, use 47K nearest value/2400 because cathode value is shared by both halves of pi =1. The output impedance may be as low as 100 ohms. The 68K resistor on the cathode is fine for a U7 and a bit lower than most cathode followers with an X7. Given 100% local current NFB, the 'U7 is OK in the cathode follower role. Therefore, the cathode follower’s bottom triode’s grid must be presented with 28% of the power supply noise, which 72k and 28k resistors yield easily enough. With R4 = 330R the first stage gain is 8. The cathode follower has a number of properties that make it useful in electronics. Apr 20, 2011 · Does anyone have a schematic for adding a balanced line output? I just want to double check what I have done on a bass amp I built for a friend. Be sure to bypass the filament's derived center tap to ground with a capacitor when elevating it. Cathode follower with tube 12au7(ECC82) Schematic. AM radio schematics). Let's use a schematic from my last post as starting point. 4mA plate current). Note both sides of the DC coupled CF are from a single 12ax7. Which also explains why the mu follower’s output is taken in between the two high value resistors and not at the top triode’s cathode or the bottom triode’s plate: mu follower output signal is pretty much equally present at all three take off points, as mu follower undergoes very little current fluctuations in the presence of an input signal. Lots of critiques to help and nobody is going to rob you on it I think. 25) = 170. 047uf, . In a nutshell, you now know why so very few cathode-follower-based power amplifiers were ever made and sold. Dec 18, 2008 · This schematic below is a simple two stage line-level preamplifier using a single 12AU7 (ECC82) tube per channel. I prefer 12AU7 (ECC82) Cathode Follower Tube Preamplifier Schematic This schematic below is a simple two stage line-level preamplifier using a single 12AU7 (ECC82) tube per channel. Cathode followers have to be designed well or there will be considerable distortion, which probably accounts for the bad reputation they have in some quarters. Here we see a input stage driving a cathode-follower output stage. General Electric A1-300 power amp. I then invented a detector using a 12AU7 cathode follower to buffer the last IFT output, then a diode to 270 pF, with 1 MΩ to -50 V dc, then 100 kΩ + 50 pF LPF, and then a second CF to buffer the detected audio signal (see Radio re-engineering, - Other misc. I'm old fashioned, sue me. If you need less gain, take a look at the RCA 12AU7 / ECC82 Cathode Follower Tube Preamp Schematic which has a gain of about 8. The Rout will be further reduced by the loop NFB for the RIAA eq. A normal 1/2 12AU7 cathode follower as used in the above 3 triode amp with passive RIAA eq will have Rout = 600r approx. Like the emitter follower, the output of the cathode follower has the same phase as the input voltage, and the voltage gain is always somewhat less than unity. 6*pi*R*C) is a better estimate for the cut-off frequency. It's a perfect match for a 600:600 output transformer. 03%. If you just need a buffer, you'll be much better served by a cathode follower. 18% THD at 10V and a rather better figure of 0. However, it does exhibit current and power gain. 5 dB with a unbypassed cathode and ≈33v/v or 30. Or similar to what I did to buffer a modified DAC using a TDA1543 (the 6111 is a low mu triode, somewhat similar to the 12AU7) Dec 26, 2013 · To prevent this, the output stage is driven by a cathode follower,based around an ECC82 valve (US equivalent: 12AU7). The cathode impedance varies from 323 Ohms to 455 Ohms. The document provides information about the Broskie Cathode Follower (BCF) PCB, including: - The BCF converts a balanced input signal to an unbalanced output signal while providing common-mode signal rejection. But many other tubes could be used. EDIT: The wiper on the pot would connect to the grid, the top of the pot would connect to the node between C2 and R6. Web First, The Cathode Follower Was Not Designed For A 12At7. 47% THD with plate follower (second stage removed) 100uF cathode bypass cap, 12ay7 tube. 2 KB · Views: 249 Lingwendil. Neither is it an aikido follower. 12AU7 (or 5814) tubes are used as cathode follower buffers between filter sections. 2 days ago · It’s pretty tight where the tubes are, as it was built as a 4S Universal initially, and then the cathode follower was added, with not a lot of room available. Thus, there was some room to voice the 834P circuit through the cathode follower section. 5uF The signal at the anode of the lower triode is fed to the grid of the cathode follower. The cathode follower distorts in a good way for us, a source follower does not have this quality so its low output impedance is its calling. Using a 27k Ohm cathode resistor, or using a CCS (constant current sink) in the cathode follower will not significantly change the output impedance of the preamp. The cathode of the follower will operate at about +100V to +120V DC, and I'm concerned this might be high enough to cause gradual degradation. My signal path is: DC coupled cathode follower 12AU7 Edcor 600:600 transformer pins 2-3 of the XLR Pin 1 goes to ground via a lift switch This is pretty much straight out of the Thunderfunk book. 42 mA at a voltage between cathode and plate of 171 V would have to be about – 8. May 10, 2012 · I employed a 12au7 triode as the reverb driver and thought to use the other half as the AC30 preamp type cathode follower. 333k. Here is the entire schematic. 014% at 2V - this makes it the clear winner. Conceptual schematics takes some working usually irl. It requires a few extra resistors and caps and the heater reference voltage is tweaked just slightly so I can sleep better. 11. Dipping into Merlin Blencowe's "Designing Tube Guitar and Bass Preamps" I found the part about rounded clipping from a cathode follower drawing grid current. I'd use the 12AX7 for both left and right channels, and a 12AU7 again for both channels. The amount applied varies with frequency and is only about 6dB at 10Hz so Rout at 10Hz at the cathode of the 12AU7 will be about Jul 21, 2011 · A 12AU7 as a cathode follower might get you a source impedance of 600R. Notice that the output is attached to the plate. Aug 30, 2013 · The bias point of the CF is set by R4, if R4 would be 100K or even lower (such as on a VOX amp), the current goes up, so does the grid current on the CF - the internal resistance (which is equal the output impedance of a CF btw. Apr 27, 2022 · To make the 12AU7 CCDA with the positive feedback to V1 cathode and NFB from output to V1 grid, you have to arrange for V1 and V2 to draw the same plate current (Ip). May 7, 2025 · With respect to my voltages while using a 12AU7 in both positions, my B+ before the 100K plate load resistor is 266 Volts, and there is 68. Dec 7, 2009 · Yes, Merlinb, I realized after posting that I forgot to include the 12BH7 stage in the cathode follower output stage in the schematic. According to the Cathode Follower calculator, with a 220kΩ cathode resistor the output impedance is only 617Ω. 4 days ago · First, the cathode follower was not designed for a 12AT7. Kagliostro's schematic is a three-stage preamp instead of the usual two-stage 5E3. 12AU7 with bypassed cathode has gain of 15. 5kΩ to 65kΩ depending on volume setting. Oct 22, 2008 · Small signal pentodes usually have a lowish plate voltage, so there is no problem with DC coupling to a CF stage. 12AU7 cathode follower will happily drive 600-ohms. But in reality, you could go anywhere from 250v to about 330v on the power supply without any issues. After all I had a cathode-follower in my mind originally. 5 = 320 ohms. Engineering and Intuition Serving the Soul of Music 86008, 2106 33 Ave. It sounds quite good. The gain will be ½ the mu of the triode at the operational point of B+/2 for each triode with a cathode resistor of 150R. The design is simple with few components, but both the tone control and filter circuit deteriorates the sound details a lot also so many switch contacts inserted further down grade the sound quality , clone results from different DIYers varies. cathode-coupled) amplifier I am a big fan of the common-cathode amplifier (also known as the “cathode-coupled” or “grounded-grid” amplifier—no thanks to Bruce Rozenblit, whose taxonomic howler has made already murky waters murkier still). Feb 10, 2011 · Well, there's the cathode follower circuit, plate tied to around 180VDC, cathode resistor 10K, and grid biased to ground thru a half megohm resistor. You need to double the transconductance and half the plate resistance or pick a high transconductance tube like a 7308. 5kΩ. This schematic shows a cathode follower circuit using a 12au7 vacuum tube with associated resistors and capacitors. The overall gain is about 8 times. The circuit steps down a high positive voltage to a lower output voltage while providing current amplification. The obvious tube choices are the 6CG7, 6DJ8, 12AU7, 12BH7, and ECC99. Feb 16, 2007 · Dear Sirs, I am using a line stage consisting in a pot followed by a 12AU7(ECC82) in a cathode-follower configuration. Apr 18, 2013 · For the 12AU7, this means as low as I'd probably go is 100 volts between the plate and cathode of the 12AU7 and at -4V grid. Member. This will get rid of 1 coupling cap and 2 resistors. The input stage would have to deliver plus and minus voltage swings of 300V to get full output from the cathode Jan 3, 2021 · OK, that makes sense that it would be a power supply issue. 4A. Safer version of the Aikido Amplifier. If you'd like something with just a little more nerd sprinkled on top (and an extra 12AU7), try the following. In the schematic below, we see a simple fixed-bias cathode follower that relies on a two-resistor voltage divider to establish the DC bias voltage for the cathode follower’s grid. The "cathode bias resistor" is an LED. Dec 20, 2021 · Va=233V (50V or so lower than the schematic, but its the transformer etc I had to hand) Va-k=103V Vg-k=-2. If direct coupling, the above will put about 104V on the grid of the EL86 cathode follower. I will be building this design with a B+ of 300V and 12AU7 tubes. Aug 20, 2024 · 12Au7 Cathode Follower Schematic. png. F. From the RCA 12au7 datasheet, what is the output impedance of a 12au7 cathode follower? mu = 19. Feb 18, 2016 · This is a DC coupled cathode follower, taken from this page and in context of the page, its how the 5F6-A Bassman drove the tone stack. The heart of Marantz 7 M7 line amp is a two common cathode stage with negative feedback followed by a cathode follower. two stage 12au7 cathode follower schematicCathode follower schematic circuit features click diagram description below special. By the way, here are the values for the output transformer: Input impedance = 11. Jan 22, 2024 · I don't know SRPP stuff in detail but output Z here should be basically that of a cathode follower. One 12AU7 is a part-watt, or can be "unloaded" for pure voltage gain. Cathode follower schematic circuit features click diagram description below special 12ax7 schematic tube amp preamp preamplifier bass circuit diy kit vacuum audio amplifier valve electronics diyaudioprojects diagram line tubes schéma The 12au7 “color” preamp with improved buffer Cathode follower with tube 12au7 (ecc82) schematic: +250vdc +b Mar 14, 2020 · The differential input stage DC couples to a cathode-coupled amplifier, which in turn DC couples to a cathode follower. Driving 600 ohms you can only get around 600/10,000= 0. One is direct coupling between the plate of the 6SJ7 and the grid of the 6V6. The cathode follower half of the Aikido amplifier Having looked into the first half of the Aikido amplifier, let’s now move on to the second half: the cathode follower portion. I have been told that substituting my present Philips Miniwatt for a mil spec tube like the 5814A, others things remaining unchanged, I will get a more powerful and defined May 7, 2012 · This is what a standard triode gain stage looks like on a schematic. It has a very high input impedance and very low output impedance. This XL version uses a White Cathode Follower buffer for about half the output impedance of the vanilla version. This splits the difference of the follower's cathode potential and the 12AX7's cathode potential (which is near zero). Feb 8, 2010 · 6. The advantage of fixed-biasing is that the input (and output) impedance is more constant with frequency and with loading. Jan 6, 2023 · 12AU7-Cathode-Follower-Schematic. The most useful characteristic of the cathode follower is its relatively low output resistance. e. Joined 2008. I tried a variety of different transformers Resistor R7 (the extra cathode resistor) is optional, although highly recommended, as its inclusion buffers the cathode follower’s output from heavy capacitive loads and increases the cathode follower’s linearity, but at the cost of increased output impedance. The overall voltage gain of the circuit is about 8. If you really need line stage gain, the linked PCB will work fine, with 12BH7s populating the sockets. James tone-stack has gain of 20:1. Oct 19, 2022 · The cathode follower is analogous to the BJT emitter follower. 5 + 1) = 0. k. With the volume control on the output, it has an output impedance that varies between about 2. The Cathode Follower A Quick Overview Right after the Grounded Cathode amplifier, the second most common tube circuit in use is the Cathode Follower. Mar 18, 2024 · 12au7 cathode follower schematic. Oct 11, 2014 · Power supply will be 90V. 2V grid bias (4. I don’t think it is power supply related, as the original 4S was pretty much dead silent except for a bit of tube rush at full volume. 5 Volts on the plate after the 100K plate load resistor. This is easily done with a potential divider from the HT. The cathode follower then drives the highly reactive RIAA equalization network, which includes the added 50kHz inflection frequency. Thats probably what, 400 ohms or something? The very loose rule of impedances is the load should be 10x or more the source so assuming a 400 ohm output impedance, the grid resistor shouldn't be lower than a 4. Your schematic indicates 2. The cathode resistor for V2 will be the same value. Better yet would be a 5687 or 6N6P, since those have lower plate resistance, so can drive 10k with relative ease. A schematic of the non-functional amp as it sits now is attached. ” From reading whatever I could find, it seems a 12au7 cathode follower usually has a very low impedance, like below 600ohms. I think this is correct. I decided on the cathode follower mostly because of the simplicity of the circuit. 5k ohm Output impedance = 133 ohm Jan 31, 2016 · You can change the source impedance to the stacks. But a 12AU7 already has a low output impedance, especially if you have a low value plate resistor. As for the 2V bias on the DAC output, you could use a coupling cap to the 12AX7. This is done by splitting the previous stage's anode resistor into two equal parts and connecting a capacitor from the cathode follower's cathode, to the junction of the two resistors [see right]. 05uf, 10uf), but not yet done the 3-section (20-20-40) filter cap. 91 in CF mode. Nov 4, 2024 · 12au7 supply cathode power follower 90v calculating using diyaudio gainclone tubes schematics finished also12au7 schematic 12ax7 preamp preamplifier amplifier schematics vacuum tubed diyaudioprojects ecc82 cathode 6sl7 Cathode follower tube tubes voltage work something better would like volts only12ax7 cathode follower schematic. Sep 25, 2017 · You can sub a 12AU7 in the cathode follower buffer spot with no changes to the circuit. Two stage 12au7 preamplifier with low impedance output stage. Pretend the cathode follower is a Fender split-load inverter without a plate load. Why? Some just prefer the sound from octal tubes, such as the famous 6SN7, so its absence was felt, myself included. Roll in a 12AU7 and see how you like that. A second 12AU7 is not much more cost, better THD, more reliable at this power level. Since the cathode follower has A v ≈1, and is non-inverting, the signal at its cathode will be nearly equal to that at the anode of the lower valve. New Octal Aikido Cathode Follower The noval Aikido cathode follower (ACF) PCB now has a brother: the octal ACF stereo PCB. The 73V output sets the DC voltage at the grids of the triodes forming the long-tailed-pair phase inverter. Oct 11, 2006 · Pulse cathode follower 1/2 a 12au7 doesn't make a very good cathode follower. Second, your schematic indicates a 12AT7. Feb 16, 2007 · the web is full of it, if you are familiar with the foreplay preamps using 12AU7's, using an IRF820 as fource follower, you can make a 1 tube preamp To be minimalist at a maximum degree, an IRF820 buffer should suffice in my case, as I do not need voltage gain. If a 6DJ8 is used, and if a low B+ voltage is used, say 150Vdc, then we can probably get away with it, as the cathode follower's cathode will not be at too high a voltage to exceed the cathode-to-heater maximum voltage. Because the cathode follower has close to unity gain, the signal voltage at the top of the load resistance will be almost the same as that at the bottom, so almost no signal current is wasted through it;- they have been "bootstrapped" and the cathode Oct 6, 2020 · When we determine what load a cathode follower can drive, we use the DC resistance between the cathode and ground for the DC load line like Valve Wizard did. There are two features that give this amplifier its superior performance. 7k to ensure its not excessively Feb 24, 2025 · 12AU7 cathode follower type amplifier made by Radio Shack circa 1960s, presently not working. Apr 16, 2025 · So that would give a cathode to plate voltage of 300 – (5. 8 + 123. Is this okay? Here is the schematic of the 12au7 tube preamp i came up with (sorry about the over. Better go with a ECC82 / 12AU7 / 5814A. 3. BTW, schematic was recommended by Bruce Rozentblitz. Jul 18, 2011 · 1) The AC-coupled cathode follower is used to couple a high output impedance circuit to a low input impedance circuit with minimal signal loss. The output stage of the circuit is a Cathode Follower and is suitable to drive a low impedance amplifier. The Quad II pre-amp and power amp. I am glad at least the Aikido PS1 is adequate for a PSU. May 29, 2020 · Any tube will do in that position, a cathode follower is a topology that doesnt provide "colour" to the sound, you could even put a wimpy 12ax7 (requires changing cathode resistor like any other different tube) because the driver requeriments of a 6y6 in that configuration are not very high, if you have 6n1p, 6n6p, 12au7, 6sn7, ecc88 variants they will all be equally good in that position. I've DC coupled a 5879 to a 12AU7 before (in a circuit using Merlin's morph control but with the triode coupling mode buffered from the CF) - schematic attached (with voltages. Lets leave aside the silly topic about the source. The classical direct coupled cathode follower takes no grid current. Apr 16, 2023 · DC coupling the cathode follower would only require 33K cathode resistor for about the same anode current, possibly slightly higher. 2) The document describes the design of an AC-coupled cathode follower circuit using an ECC82 tube to act as a buffer for a guitar amplifier's effects loop. May 9, 2020 · I've modeled 12AT7 and 12AU7 cathode followers into a 10k load, and they'll suffice. La 12ax7 a un mu de 100 un gain plus elevé que la 12au7 qui est de 17 et il y aurais des modifications a faire en tout ou en parties. 2023-01-13 10:10 pm #13 2023-01-13 10:10 pm #13 A better choice may be 4 days ago · However in my travels online for a solution, I noticed that on this site the 12AX7's and other similar valves were used in linestage designs postedand that the 12AU7 (ECC82) Cathode Follower Tube Preamplifier Schematic - as listed in this site - appears to show promise in being able to be used/modified into the cathode follower stage of the 6 days ago · You’ll note that I have the B+ listed at 300v. This device, as opposed to a transistor configuration, enables the output stage to be driven with a constant value, low impedance. Actually, in keeping with the first law of engineering (“Nothing of value comes without a cost”), this extra resistor’s added benefits must be paid for with a higher output impedance and slightly less voltage and current swing. Wiring capacitance will likely be about 5 pf. The bottom of the pot would go to ground. A lot of the time the bias resistor is ignored when Rk is significantly larger. Fixed Biased Cathode Follower The other way to bias the cathode follower is by applying a fixed voltage to the grid. This is a good simple design that will provide 12 watts. For a partially bypassed cathode, the frequency at 1/(2*pi*R*C) is where the gain has risen a certain amount above the unbypassed gain. 4dB with a bypassed Nov 23, 2019 · So 2 standerd 12ax7/ecc83 gain stages that are capacitor coupled followed by a direct coupled cathode follower using the ECC88. In fact output impedance will be something like 420 ohms. A 12AU7 has 2200 to 3100 uMhos. The gain for the above circuit is: Av = 19. _____ Mar 6, 2023 · 2. It was designed ONLY for a 12AU7. I have replaced three elderly caps (. Jun 2, 2014 · Trio, LeeStereo, both great posts. This is a high gain preamplifier that is suitable for use where a lot of gain is required - to drive a power amplifier that needs plenty of gain or perhaps for use with instruments, like a guitar or microphone. If you are using this in the preamp stage, the gain will be about ≈21v/v or 26. 2k for cathode For Quad 6146-based PPP (for amp see schematic below) Small Regulated Bench Supply. May 8, 2012 · This is a high gain preamplifier that is suitable for use where a lot of gain is required - to drive a power amplifier that needs plenty of gain or perhaps for use with instruments, like a guitar or microphone. Exactly why that would be I don't know. The problem with taking a FX send from the cathode of a stage that is being overdriven is that the cathode signal is not the same as the anode signal. The plate of the 12AU7 used for a cathode follower is at 266 Volts as well. 7. kxvr lpu lomgsxk dzabpsn ydsg omzubf kdzjt ehkplrun hflrl pwyrh